Firefox is beaten EASILY by Opera's browsers, Google's browser, and even Apple's browser. In terms of customizing, firefox is the best, but it's not even remotely close to being the fastest.
And benchmark testing shows Opera 11 beta being on top for now (soon to be beaten by Chrome again).
Chrome is an excellent browser and in my opinion the fastest that exists. In terms of speed it proves to be very pleasing. I admit Opera is fast, but there something about the way it works that I don't quite like.